Microhardness Gradients and Structural Phase States of the Coating Contact Zone (HEA CoCrFeNiAl) with Substrate (Alloy 5083)

A non-equiatomic high-entropy alloy (HEA) CoCrFeNiAl coating on the 5083 alloy substrate is produced by wire-arc additive manufacturing (WAAM). It is revealed that microhardness changes significantly at the contact zone of the "coating — substrate" system. The changes range from 7.6 GPa at the coating boundary and the contact zone up to 1.6 GPa at the substrate boundary and the contact zone. The coating and substrate have the microhardness values of 6.3 GPa and 1.1 GPa, respectively. The structural phase state, defective structure, and elemental composition of the “coating — substrate” system are analyzed using methods of modern physical material science. It is shown that they depend on the distance from the contact zone between the coating and substrate. Also, it is found out that application of the high-entropy coating on the 5083 alloy surface is accompanied by mutual alloying of the coating and substrate. Creation of two types of submicro- and nanosized particles is revealed in the study. Nanosize particles of Al2O3 and MgAlO oxides, Al and HEA subgrains form the first structure. The second structure consists of nanosized HEA subgrains, Al13Fe4 and (NiCo)3Al4 nanoparticles located along the grain boundaries.